This chapter is built from the official PCTB textbook Computer Science and Entrepreneurship, Class 9 (based on the Revised National Curriculum of Pakistan 2023, approved by the Punjab Curriculum and Textbook Board, Lahore). The exercise questions below are the book's own exercise questions; the answers are model answers written for this guide.
Chapter titles and exercise questions are taken from the official book's contents and exercise pages. No page numbers are claimed for individual questions.
An analog signal changes smoothly and continuously and can take any value in a range — for example the sound of a voice or body temperature. A digital signal has only two values, 0 and 1, and is used by computers and digital electronics.
An ADC (Analog to Digital Converter) turns an analog signal into digital form so a computer can process it (for example a microphone). A DAC (Digital to Analog Converter) does the reverse, for example turning digital music into sound from a speaker.
اینالاگ سگنل مسلسل اور ہموار تبدیل ہوتا ہے اور کسی بھی قدر لے سکتا ہے جیسے آواز یا جسمانی درجہ حرارت۔ ڈیجیٹل سگنل میں صرف دو قدریں ہوتی ہیں: 0 اور 1۔ اے ڈی سی اینالاگ سگنل کو ڈیجیٹل میں بدلتا ہے تاکہ کمپیوٹر اسے پراسیس کر سکے، اور ڈی اے سی ڈیجیٹل کو واپس اینالاگ آواز میں بدلتا ہے۔
In Boolean algebra every value is TRUE (1) or FALSE (0). AND (·) is true only when both inputs are true; OR (+) is true when at least one input is true; NOT (¯) flips the value. A truth table lists every combination of inputs and the resulting output.
Boolean laws simplify expressions: for example A + 0 = A (identity), A + 1 = 1 (null law), A + A = A, and De Morgan's theorems, which say the NOT of an AND is the OR of the NOTs, and vice versa. Simplifying a circuit means fewer gates, lower cost and faster operation.
بولین الجبرا میں ہر قدر درست (1) یا غلط (0) ہوتی ہے۔ AND تب درست جب دونوں ان پٹ درست ہوں، OR تب درست جب کم از کم ایک درست ہو، اور NOT قدر کو الٹ دیتا ہے۔ ٹرتھ ٹیبل ان پٹ کے ہر مجموعے اور نتیجے کو درج کرتا ہے۔ بولین قوانین سے ایکسپریشن سادہ کیا جاتا ہے جس سے سرکٹ میں گیٹس کم لگتے ہیں۔
Effective troubleshooting is systematic, not guesswork. The seven steps are: (1) Identify the problem, (2) Establish a theory of probable cause, (3) Test the theory to determine the cause, (4) Establish a plan of action to resolve it, (5) Implement the solution, (6) Verify full system functionality, and (7) Document findings, actions and outcomes.
Testing a theory matters because it stops you fixing the wrong thing. Verifying after the fix matters because a problem can look fixed while another fault remains. Documentation helps the next person solve the same problem faster.
موثر ٹربل شوٹنگ اندازے سے نہیں بلکہ منظم طریقے سے ہوتی ہے: (1) مسئلہ پہچانو، (2) ممکنہ وجہ کا نظریہ بناؤ، (3) نظریے کو جانچو، (4) حل کا منصوبہ بناؤ، (5) حل نافذ کرو، (6) پورے سسٹم کی کارکردگی کی تصدیق کرو، (7) نتائج اور اقدامات درج کرو۔ نظریے کی جانچ غلط چیز ٹھیک کرنے سے بچاتی ہے اور دستاویز اگلے شخص کی مدد کرتی ہے۔
Common hardware faults include failing RAM (random crashes or blue screens), a failing hard drive (strange noises, missing files, very slow access) and loose or damaged cables. Replacing a faulty component, or upgrading it, is part of troubleshooting — but only after the cause has been tested.
Backups protect data when hardware fails: keep copies on an external drive or in the cloud, and test that you can restore them. A safe, organised workspace — tidy cables, good ventilation, no food or drink over the keyboard — prevents many faults before they start.
عام ہارڈ ویئر خرابیوں میں خراب RAM (اچانک کریش)، خراب ہارڈ ڈرائیو (عجیب آوازیں، فائلیں غائب) اور ڈھیلے کیبل شامل ہیں۔ وجہ کی جانچ کے بعد خراب پرزہ بدلا یا اپ گریڈ کیا جاتا ہے۔ بیک اپ ڈیٹا کو بچاتا ہے: نقل بیرونی ڈرائیو یا کلاؤڈ میں رکھیں اور بحالی کی جانچ کریں۔ صاف اور ہوادار کام کی جگہ بہت سی خرابیوں سے پہلے ہی بچا لیتی ہے۔
اس chapter کی exercise میں book کے MCQs, short questions اور long questions ہیں — تمام سوال کتاب کی exercise کے ہیں, جواب کے ساتھ.
1. Which of the following Boolean expressions represents the OR operation?
Answer: (b) — OR is written A + B; AND is A · B.
2. What is the dual of the Boolean expression A . 0 = 0?
Answer: (a) — The dual swaps AND with OR and 0 with 1, so A · 0 = 0 becomes A + 1 = 1.
3. Which logic gate outputs true only if both inputs are true?
Answer: (b) — AND outputs true only when both inputs are true.
4. What is the decimal equivalent of the binary number 1101?
Answer: (c) — 1101 in binary = 8 + 4 + 0 + 1 = 13.
5. What is the first step in the systematic process of troubleshooting?
Answer: (c) — The first troubleshooting step is to identify the problem.
6. Why is effective troubleshooting important for maintaining systems?
Answer: (c) — Effective troubleshooting keeps systems operating smoothly and efficiently.
7. Which step involves coming up with a theory about what might be causing a problem?
Answer: (b) — Coming up with a theory is the 'Establish a Theory of Probable Cause' step.
8. After implementing a solution, what is the next step in the troubleshooting process?
Answer: (c) — After implementing a solution, the next step is to verify full system functionality.
9. Why is troubleshooting important in computing systems?
Answer: (c) — Troubleshooting keeps systems running smoothly and securely.
Answer: A Boolean function is an expression built from Boolean variables (0/1) and operators (AND, OR, NOT) that gives a 0 or 1 output for every combination of inputs.
Answer: A truth table lists every possible input combination and its output, so it verifies that a logic design does exactly what is intended and exposes errors.
Answer: A NOT gate inverts its input: 0 becomes 1 and 1 becomes 0. Truth table: input 0 → output 1; input 1 → output 0.
Answer: ADC converts an analog signal (for example from a microphone) into digital form for a computer; DAC converts digital data back into analog form (for example to a speaker).
Answer: AND truth table for A, B: 0,0 → 0; 0,1 → 0; 1,0 → 0; 1,1 → 1. Only 1 AND 1 gives 1.
Answer: The first step is to identify the problem: what exactly is wrong, when does it happen, and what has changed?
Answer: After identifying the problem, establish a theory of probable cause — a reasoned guess about what is causing it.
Answer: Testing a theory confirms (or rules out) the suspected cause before you change anything, so you do not waste time fixing the wrong thing.
Answer: Implementing the solution means carrying out the planned fix — for example replacing a faulty part, updating software or changing a setting — while following safety and escalation procedures.
Answer: Verification proves the problem is fully solved and that the fix has not caused a new problem elsewhere in the system.
Answer: Computers are built from Boolean logic: AND, OR and NOT gates combine to make circuits that add, compare, store and choose. Boolean operations decide conditions in programs (if this AND that), control hardware (a light switches on only when two switches are on — an AND), and simplify circuits so fewer gates are needed, which means lower cost, less power and faster operation.
Answer: As printed, F(A, B) = A·B + A·B = A·B by the idempotent law (A + A = A). Note: in the common textbook form the second term is A·B with a bar over B (A AND NOT B); then F = A·B + A·B̅ = A·(B + B̅) = A·1 = A. Either way, the expression simplifies to a single term — which is the point of Boolean simplification.
Answer: Troubleshooting matters because computers fail, and downtime costs time, work and sometimes data. Systematic troubleshooting finds the real cause instead of guessing, prevents repeated failures, protects data (through backups made before risky fixes), and keeps systems secure — an unexamined fault can be a security hole. Good troubleshooting also saves money: many faults are fixed in minutes once the cause is known.
Answer: The seven steps are: (1) Identify the problem — gather symptoms, ask what changed. (2) Establish a theory of probable cause — the most likely explanation. (3) Test the theory — check the suspected part or setting; if the test fails, revise the theory. (4) Establish a plan of action — decide the fix and its risks, including backups. (5) Implement the solution — carry out the fix. (6) Verify full system functionality — test the whole system, not just the symptom. (7) Document findings, actions and outcomes — write what was wrong and what fixed it, for next time.
Answer: Documentation turns a one-off fix into reusable knowledge: the next person with the same fault finds the cause and fix immediately instead of repeating the whole diagnosis. It also proves what was done (important in workplaces and exams), reveals repeated faults that point to a deeper problem, and helps train new technicians.
Answer: Common backup methods: full backup (a complete copy of everything — simple to restore, but slow and large); incremental backup (only what changed since the last backup — fast and small, but restore needs the full backup plus every increment); differential backup (everything changed since the last full backup — a middle path); and cloud/online backup (copies stored off-site, protected from fire or theft, but needing internet). The safest practice combines a regular full backup with frequent incremental backups, plus an off-site copy.
Analog signals vary continuously while digital signals use only 0 and 1; Boolean AND, OR and NOT gates build all digital logic; and troubleshooting follows seven steps from identifying the problem to documenting the fix.
Revision guidance: پہلے MCQs خود حل کرو, پھر جواب ملاؤ; short سوالوں کے جواب اپنے الفاظ میں لکھ کر practice کرو; long سوالوں کے لیے ہر section کی headings اور مثالیں یاد رکھو.
اینالاگ سگنل مسلسل بدلتا ہے جبکہ ڈیجیٹل میں صرف 0 اور 1 ہوتے ہیں؛ AND، OR اور NOT گیٹس سے تمام ڈیجیٹل لاجک بنتی ہے؛ اور ٹربل شوٹنگ مسئلے کی شناخت سے لے کر دستاویز تک سات مراحل میں ہوتی ہے۔
رہنمائی: پہلے ایم سی کیوز خود حل کریں پھر جوابات ملائیں؛ مختصر سوالات کے جوابات اپنے الفاظ میں لکھ کر مشق کریں؛ تفصیلی سوالات کے لیے ہر سیکشن کی سرخیاں اور مثالیں یاد رکھیں۔
Is chapter ke topics: Analog and Digital Signals — ADC and DAC · Boolean Algebra, Logic Gates and Truth Tables · Troubleshooting: A Systematic 7-Step Process · Hardware, Backups and a Safe Workspace · مشق
Topics (Urdu): اینالاگ اور ڈیجیٹل سگنلز — اے ڈی سی اور ڈی اے سی · بولین الجبرا، لاجک گیٹس اور ٹرتھ ٹیبلز · ٹربل شوٹنگ: منظم 7 مراحل کا عمل · ہارڈ ویئر، بیک اپ اور محفوظ کام کی جگہ
Revision guidance: پہلے MCQs خود حل کرو, پھر جواب ملاؤ; short سوالوں کے جواب اپنے الفاظ میں لکھ کر practice کرو; long سوالوں کے لیے ہر section کی headings اور مثالیں یاد رکھو.
Chapter-wise tests, fresh random papers اور instant score کے لیے PunjabTest.com کا میں test section دیکھو:
PunjabTest.com — Complete Guide Book • Class 9 Computer Science, Chapter 2 (official PCTB book exercise, Session 2026–27) • English + Urdu